1. Field of the Invention
The present invention relates to the technical field of sensors area.
More precisely, the present invention concerns a system and a method to improve the morphology discrimination of a passenger seated in an automotive seat fitted with several capacitive sensors.
A non exclusive implementation of the present invention relates to control the airbag triggering in a car.
2. Description of Related Art
In the last past years, airbag in automotive area were triggered, in case of shock, by means of an accelerometer. This basic triggering didn't take in account the occupant morphology (child, small adult, medium adult, and large adult).
Generally known airbags were triggered even if the seat is empty or occupied by a baby seated in a “CRS” (Child Restrain Seat). This last case very serious is the cause of numerous deaths.
For these reasons henceforth some vehicles are fitted out with a switch allowing disabling airbag triggering when a CRS is mounted in seat. This switch is linked with a light indicator situated on dashboard showing the state of airbag device triggering: “on” state or “off” state.
Since year 2003 a most restricting regulation was launched in US (FMV SS 208 regulation) compelling car manufacturer to fit out at least a third part of global car production with a detecting passenger device called “OCS” (Occupant Classification System).
It is noticed that the airbag must not be triggered in the following conditions:                If the seat is empty,        If the seat is occupied by a baby seated in CRS,        if the seat is occupied by a child less 6 years old (less than 26 kg).        
Independently regulations which will be set, business constraints all over the world, lay down an airbag smart triggering; that is to mean:                No air bag triggering:        for an empty seat,        for a seat occupied by a baby seated in CRS,        for a seat occupied by a child less 6 years old (less than 26 kg),        Monitoring the airbag power according to occupant morphology defined as following:        5th percentile class (46-53 kg/1.40-1.65 m) linked to small adult,        50th percentile class (68-73 kg/1.70-1.8 m) linked to medium adult,        95th percentile class (94-98 kg/1.83-1.93 m) linked to large adult.        
However at the present time no system or method offers a fully satisfactory solution for that.
The Applicant has filed on Jul. 28, 2005 a French patent application under number FR-0508072, which describes a technical structure of a capacitive sensor allowing detecting if the sensor is covered or not by a target.
The Applicant has also filed on May 17, 2006 a European patent application under number EP06290806.6, which describes a method for determining the surface of a capacitive sensor covered by a target and the distance separating said target and said capacitive sensor and has filed on May 17, 2006 a European patent application under number EP06290807.4, which describes a method for determining the morphology of an occupant in an automotive seat with capacitive sensors. These methods are well suited for operation under standard range of temperature and humidity.
But in practice, some constraints may disturb the discrimination of passenger.
Not restrictively such constraints may be due to a wet obstacle present on the seat, such for example in the case of a passenger (adult or child) seated with a wet raincoat, a passenger coming from beach putting a damp towel on seat before sitting on it, beverage dropping damping partial surface of seat or a shower leading to a damped seat if the window pane is bad shut.
Other constraints may be due to no human occupation on the seat, like metallic object, suit case, pack of bottles of water, etc. provided on the seat.